1. Field of the Invention
The present invention relates to a temperature control apparatus and a temperature control method, and more particularly to a temperature control apparatus, a processing apparatus provided with the temperature control apparatus and a temperature control method for controlling, by a resistance heater having the characteristic such that its resistance value changes dependently on a temperature, the temperature of a member provided with the resistance heater.
2. Description of Related Art
In recent years, a fuel cell has attracted attention as a clean power source having high energy conversion efficiency, and the practical application of the fuel cell to a fuel cell powered vehicle, an electric home, and the like, has been advanced. Moreover, the research and development for using a fuel cell as a power source also in portable electronic equipment, such as a cellular phone and a notebook-size personal computer, has advanced.
A fuel cell is a device for producing electric power by electrochemical reactions between hydrogen and oxygen. The hydrogen to be supplied to the fuel cell is produced from, for example, a liquid fuel, such as methanol. In this case, a reaction apparatus for producing the hydrogen from a liquid fuel and water is connected to the fuel cell.
The reaction apparatus is composed of, for example, a vaporizer vaporizing a liquid fuel and water, a reformer causing the reforming reaction of the vaporized fuel and water to produce hydrogen, and a carbon monoxide remover removing the carbon monoxide infinitesimally produced in the reformer by means of the oxidization thereof. As such a reaction apparatus, a reaction apparatus integrally forming the reformer and the carbon monoxide remover was also developed. For example, a reaction apparatus composed of a joined body of a plurality of substrates exists, the reaction apparatus configured as follows: grooves are formed on the joint surfaces of these substrates; catalysts are carried on the wall surfaces of the grooves; and the substrates are joined with one another so that the grooves may be covered by the substrates to function as the flow paths of the reformer and the carbon monoxide remover.
Now, the temperatures in the reformer and the carbon monoxide remover are set to the temperatures suitable for the respective reactions (optimum temperatures) in order that desired reactions may be efficiently caused in each chamber. Because the optimum temperatures are higher than a room temperature, it is necessary to heat the reformer and the carbon monoxide remover. Moreover, because the reformer and the carbon monoxide remover must be kept at the respective optimum temperatures during being in use, it becomes necessary to control them to keep their temperatures at the optimum temperatures by controlling their temperatures from time to time.
In order to keep the temperatures of the reformer and the carbon monoxide remover at the optimum temperatures, it is general to use a feedback control method. That is, the reformer and the carbon monoxide remover are heated by a resistance heater; the temperatures of the reformer and the carbon monoxide remover are measured with temperature sensors, such as thermocouples; the measured temperatures are fed back; and the supply power to be supplied to the resistance heater is controlled on the basis of the measured temperatures with the temperature sensor. The reformer and the carbon monoxide remover can be thereby kept at the optimum temperatures.
Moreover, if the resistance value of the resistance heater depends on the temperature, then the temperature can be measured on the basis of the resistance value of the resistance heater. The resistance heater can be used also as a temperature sensor accordingly, and the temperature sensor can be omitted.
In this case, there is a method of controlling the temperature of the resistance heater by controlling the current flowing through the resistance heater as the voltage across the resistance heater (response voltage) is being measured with an operational amplifier. In this case, the current value of the current flowing through the resistance heater is set; the current of the current value is flown through the resistance heater; and the voltage of the resistance heater is measured with the operational amplifier to be fed back. The resistance value of the resistance heater is then obtained from the set current value of the current and the measured voltage. Moreover, the temperature of the resistance heater is also obtained from the obtained resistance value of the resistance heater. In order to set the resistance heater at a desired set temperature, the current value of the current flowing through the resistance heater is newly set on the basis of the obtained resistance value or the obtained temperature, and the current of the newly set current value is flown through the resistance heater.
However, because a certain power source voltage is generally applied to a circuit including a resistance heater, it is led to connect a variable resistance in series with the resistance heater to adjust the resistance value of the variable resistance in order to adjust the current flowing through the resistance heater. In this case, useless electric power is consumed at the part of the variable resistance, and power efficiency falls. In addition, heat generation is caused by the consumption of the useless electric power, and the accuracy of temperature control sometimes falls.
Moreover, if the current of the resistance heater is enlarged, then the response voltage of the resistance heater also becomes larger. It becomes necessary to widen the range of the input voltage of operation amplifier for measuring the response voltage of the resistance heater, or to divide the input voltage and to attenuate the divided voltages in respective voltage ranges with an attenuator or the like, accordingly. The resolution of the measurement of the response voltage of the resistance heater falls and the causes of errors of the measurement increase.